In the proposed research, the function of sperm membrane autoantigens during fettilization will be determined using mouse fertilization, both in vitro and in vivo. A set of intrinsic sperm membrane autoantigens, selected on the basis of an effect upon sperm function during fertilization, will be defined with the aid of monoclonal antibodies produced by syngeneic immunization with mouse testis membranes. Furthermore, the behavior of the specific functional autoantigens during capacitation, zona binding, acrosome reaction induction, zona penetration and sperm-egg membrane fusion will be assessed by labeled monoclonal antibody probes. Finally, the lipid composition of the sperm plasma membrane will be altered to determine the role of sperm plasma membrane lipid during fertilization. The significance of this proposal lies in its examination of individual sperm membrane autoantigens with defined functions during specific, separable, steps of the fertilization process in the mouse.